The present invention relates to electronic imaging systems and, more particularly, to electronic imaging system with improved auto-focus control.
Recently, electronic still cameras or like electronic imaging systems are popularly used, which utilizes a CCD or like imaging device for photoelectrically converting a scene image focused thereon by a photographic optical system to an electric image signal to be recorded on a recording medium or the like.
Such an electronic imaging system usually comprises an auto-focusing means (hereinafter referred to as AF means) including a focus detecting means and effective auto-focusing on the basis of the focus detection result.
A prior art auto-focusing means used for an electronic imaging system utilizes a so-called contrast detection AF means (hereinafter referred to as imager AF means), which detects the focal point of the photographic optical system by detecting the state of focus of a scene image on the basis of the difference (or contrast) of quantities of high frequency components in the image signal obtained by the imaging device. Another prior art auto-focusing means is an AF means of a so-called infrared active system (hereinafter referred to as infrared active AF means), in which the scene distance is measured by a triangular measuring method. In the triangular measuring method, an infrared light flux is emitted toward the scene, a reflected light flux therefrom is received, and the scene distance is calculated from the angle between the emitted and reflected light fluxes.
However, in an electronic imaging system with the above imager AF means, in such circumstances as a dark environment of photography or low brightness or contrast of the scene, it may sometimes be difficult to detect the state of focus of the scene image, thus possibly resulting in erroneous detection.
In order to realize the reliable focus detection even under the above circumstances, Japanese Patent Laid-Open No. 8-327891 proposes various electronic imaging systems with imager AF means, which also comprise an AF assistant light-emitting means for emitting assistant light (hereinafter referred to as AF assistant light) toward the scene. In such circumstances that erroneous focus detection may result, the AF assistant light-emitting means is controlled to emit AF assistant light toward the scene, thus always ensuring reliable focus detection.
In a focusing means disclosed in the Japanese Patent Laid-Open No. 8-327891, a light projection pattern for increasing the contrast or a predetermined frequency band of the scene, is generated according to an image signal obtained from a imaging means. In such circumstances that the scene is low in contrast or dark, the generated light projection pattern is projected toward the scene, thus increasing the contrast or the like of the scene image and greatly improving the accuracy of the focus detection.
Japanese Patent Laid-Open No. 5-2129 proposes various applications of the infrared active AF means. An electronic measuring system disclosed in this publication uses a scene distance measuring means, in which an infrared light flux or the like is emitted through a lens toward the scene, and the reflected light flux therefrom is made to be incident on a photographic optical system and thence on an imaging device (or CCD). A signal representing the scene distance is obtained from the position of incidence of light on the imaging device, size of the incident light pattern, etc., and the state of focus is detected according to the signal thus obtained.
Various further electronic imaging systems heretofore proposed comprise a plurality of AF means, which are switched to select an adequate one as desired.
However, in the above prior art electronic imaging systems performing the focus detection through the AF assistant light-emitting means or the infrared active AF means, it is necessary to supply great power to the component elements of these means.
In normal imaging operation, an imaging section of the imaging device (or CCD) is continuously driven, and this means that usually the power is always supplied to the components of the section. Therefore, depending on the circumstance of photography, the power may have to be supplied to the above AF assistant light-emitting means or the infrared active AF means while continuing the power supply to the imaging section. A power supply having a greater capacity is thus necessary.
However, in view of the portability and the ready availability, the drive power supply used for driving the prior art electronic imaging system, is usually a small-size battery such as a dry battery having relatively low capacity. Therefore, it is conceivable that when an excessive power supply state is brought about, the power supply voltage is tentatively reduced to result in an unstable state or disabling of the operation of the system itself. In addition, when the power supply to the imaging section, the AF assistant light-emitting means, the infrared active AF means, etc. is concentrated at a point, an extreme current peak increase may occur, possibly resulting in erroneous operation or operation failure.
In view of the background as described above, the present invention has an object of providing an electronic imaging system, which comprises an imager AF means and an infrared active AF means, these AF means being capable of being automatically switched to select an optimal AF means as desired, thus permitting more accurate focus detection and also power consumption saving to contribute to energy saving while always ensuring a stable power supply state.
According to a first aspect of the present invention, there is provided an electronic imaging system comprising: a photographic optical system for focusing a scene image; an imaging means for converting the scene image focused by the photographic optical system to an image signal; a high frequency component detecting means for detecting high frequency components of the image signal obtained by the imaging means; a light detecting means including a light-emitting means for emitting light toward the scene and a light-receiving means for receiving light emitted by the light-emitting means and reflected from the scene; a driving means for controlling the focal point of the photographic optical system; a brightness detecting means for detecting the brightness of the scene; and a drive control means for controlling the driving means on the basis of the output of the high frequency detecting means or the light detecting means; wherein the focal point control is performed on the basis of the output of the high frequency component detecting means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is higher than a predetermined brightness, and the focal point control is performed on the basis of the output of the light detecting means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is lower than the predetermined brightness, the output of the light detecting means being obtained by controlling a power supply to cut off current or supply a relatively low current flowing in the imaging means and then driving the light detecting means for emission of light toward the scene and reception of light reflected light from the scene.
According to a second aspect of the present invention, there is provided an electronic imaging system comprising: a photographic optical system for focusing a scene image; an imaging means for converting the scene image focused by the photographic optical system to an image signal; an image display means for displaying the image signal obtained by the imaging means; a recording means for recording the image signal obtained by the imaging means; a high frequency component detecting means for detecting high frequency components of the image signal obtained by the imaging means; a light detecting means including a light-emitting means for emitting light toward the scene and a light-receiving means for receiving light emitted by the light-emitting means and reflected from the scene; a driving means for controlling the focal point of the photographic optical system; a brightness detecting means for detecting the brightness of the scene; and a drive control means for controlling the driving means on the basis of the output of the high frequency detecting means or the light detecting means; wherein the focal point control is performed on the basis of the output of the high frequency component detecting means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is higher than a predetermined brightness, and the focal point control is performed on the basis of the output of the light detecting means and the recorded image is displayed on the image display means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is lower than the predetermined brightness, the output of the light detecting means being obtained by controlling a power supply to cut off current or supply a relatively low current flowing in the imaging means and then driving the light detecting means for emission of light toward the scene and reception of light reflected light from the scene.
According to a third aspect of the present invention, there is provided an electronic imaging system which further comprises: a photographic optical system for focusing a scene image; an imaging means for converting the scene image focused by the photographic optical system to an image signal; a high frequency component detecting means for detecting high frequency components of the image signal obtained by the imaging means; a light detecting means including a light-emitting means for emitting light toward the scene and a light-receiving means for receiving light emitted by the light-emitting means and reflected from the scene; a driving means for controlling the focal point of the photographic optical system; a brightness detecting means for detecting the brightness of the scene; and a drive control means for controlling the driving means on the basis of the output of the high frequency detecting means or the light detecting means; and a battery voltage detecting means for detecting the voltage of a power supply battery; wherein the focal point control is performed on the basis of the output of the high frequency component detecting means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is higher than a predetermined brightness, and the focal point control is performed on the basis of the output of the light detecting means when detecting, from the result of detection in the brightness detecting means, that the brightness of the scene is lower than the predetermined brightness, and also detecting that the result of detection in the battery voltage detecting means is lower than a predetermined value, the output of the light detecting means being obtained by controlling the power supply battery to cut off current or supply a relatively low current flowing in the imaging means and then driving the light detecting means for emission of light toward the scene and reception of light reflected from the scene.